1. Field of the Invention
The present invention relates to a developing apparatus including a developer carrying member and a rotatable developer supplying member for supplying a developer to the developer carrying member and also relates to an image forming apparatus including the developing apparatus. The developing apparatus can be used in an electrophotographic apparatus such as a printer or a copying machine.
The device illustrated in FIG. 14 is known as a device for detecting a remaining amount of the developer (hereinafter, referred to as toner) in a developing apparatus used in an image forming apparatus such as an electrophotographic apparatus. The device is described in more detail. A magnetic mono-component developer (magnetic toner) as the developer contained in a developing container 71 is fed to a developing chamber 73 by a toner feeding member 72. In the developing chamber 73, a sleeve 75 incorporating a stationary magnet 74 and rotating in a direction indicated by the arrow of FIG. 14 is provided while facing a photosensitive drum 76. In order to coat the surface of the sleeve 75 with the toner fed to the developing chamber 73, an elastic blade 77 is provided. The sleeve 75 and the photosensitive drum 76 are separated from each other at an interval of 50 μm to 500 μm, and the surface of the sleeve 75 is coated with the toner of a thickness smaller than the interval by the elastic blade 77. The sleeve 75 is applied with a developing bias generated by superimposing an alternating voltage on a direct voltage by a developing bias power source 101, so so-called jumping development is effected between the sleeve 75 and the photosensitive drum 76.
The toner remaining amount detecting method in the above-mentioned developing apparatus 70 will now be described. An antenna 78 formed of a metal bar made of stainless steel or the like is provided in parallel with the sleeve 75. When a developing bias generated by superimposing the alternating voltage on the direct voltage is applied to the sleeve 75, the voltage depending on the capacitance between the sleeve 75 and the antenna 78 is induced by the antenna 78. Thus, there is a difference in capacitance between the sleeve 75 and the antenna 78 between the state where the space therebetween filled with the toner because the toner is not consumed and the state where the space therebetween is not filled with the toner because the toner is consumed. Accordingly, the voltage induced by the antenna 78 is different in both cases. The voltage induced by the antenna 78 is detected by a detector 102.
Generally, in the developing apparatus where the nonmagnetic mono-component developer (nonmagnetic toner) is used, the developing chamber 73 is provided with a coating member. In the case where the toner remaining amount detecting method which is performed while utilizing the variation in capacitance is adopted to the developing apparatus using the nonmagnetic toner as described above, the space in which the antenna is provided is reduced owing to the coating member. As a result, there arises such a problem in that the feeding of the toner is disturbed.
In order to solve the above-mentioned problem, as illustrated in FIG. 15, there is known a method of using a supplying member for supplying the toner to the sleeve. The supplying member 80 is formed by a urethane sponge circumferentially provided around a conductive metal supporting member 79. There is also suggested a method of detecting the toner remaining amount with the induced voltage generated as follows, in which, the sleeve 75 is applied with an alternating current when coated with the toner by the supplying member, so the voltage is induced on the conductive supporting member 79 correspondingly to the amount of the developer. (Refer to Japanese Patent Application Laid-Open No. H04-234777.)
Meanwhile, as a structure of a foam layer of a supplying member there is cited the supplying member disclosed in Japanese Patent Application Laid-Open No. H11-288161, which has the foam layer with the aeration amount of 10 to 40 cc/cm2/sec., thereby preventing the deterioration of the toner to realize to an excellent image quality. However, in the above-mentioned document, the description of the toner remaining amount detection cannot be found.
There are involved the following problems in the device for detecting the remaining amount of the developer provided in the above-mentioned image forming apparatus.
In the toner remaining amount detector in which the antenna is used as illustrated in FIG. 14, it is necessary to provide the antenna dedicated to detecting the toner remaining amount, which leads to disadvantages in space and cost. In addition, the antenna largely prevents the accurate detection of the remaining amount of the toner. This is because the remaining amount of the toner cannot be detected as long as the amount of the toner present between the antenna and the sleeve is not decreased. Specifically, the same output value is obtained in each of the cases where the toner is filled in the container sufficiently while the developing apparatus is unused and where the amount of the toner present between the antenna and the sleeve is the same as that in the unused state thereof even though the toner is consumed to some extent. In order to solve this problem, it is necessary to provide another antenna in the container.
Meanwhile, in the developer remaining amount detector disclosed in Japanese Patent Application Laid-Open No. H04-234777, it is possible to omit the dedicated antenna, thereby solving the disadvantages in space and cost. However, the detection accuracy thereof remains unsatisfactory.